Access point and methods for distinguishing hew physical layer packets with backwards compatibility

ABSTRACT

Embodiments of a system and methods for distinguishing high-efficiency Wi-Fi (HEW) packets from legacy packets are generally described herein. In some embodiments, an access point may select a value for the length field of a legacy signal field (L-SIG) that is non-divisible by three for communicating with HEW stations and may select a value for the length field that is divisible by three for communicating with legacy stations. In some embodiments, the access point may select a phase rotation for application to the BPSK modulation of at least one of the first and second symbols of a subsequent signal field to distinguish a high-throughput (HT) PPDU, a very-high throughput (VHT) PPDU and an HEW PPDU.

PRIORITY CLAIM

This application claims priority under 35 U.S.C. 119(e) to U.S.Provisional Patent Application Ser. No. 61/976,951 [reference number4884.087PRV (P65769Z)] filed Apr. 8, 2014 and to U.S. Provisional PatentApplication Ser. No. 61/906,059 [reference number 4884 031PRV (P62429Z)]filed Nov. 19, 2013, each of which is incorporated herein by referencein its entirety.

TECHNICAL FIELD

Embodiments pertain to wireless networks. Some embodiments relate toWi-Fi networks and networks operating in accordance with the IEEE 802.11standards. Some embodiments relate to high-efficiency wireless orhigh-efficiency Wi-Fi (HEW) communications in accordance with the IEEE802.11ax draft standard.

BACKGROUND

IEEE 802.11ax (High Efficiency Wi-Fi (HEW)) is the successor to IEEE802.11ac standard and is intended to increase the efficiency of wirelesslocal-area networks (WLANs). HEW's goal is to provide up to four-timesor more the throughput of IEEE 802.11ac standard. HEW may beparticularly suitable in high-density hotspot and cellular offloadingscenarios with many devices competing for the wireless medium may havelow to moderate data rate requirements. The Wi-Fi standards have evolvedfrom IEEE 802.11b to IEEE 802.11g/a to IEEE 802.11n to IEEE 802.11ac andnow to IEEE 802.11ax. In each evolution of these standards, there weremechanisms to afford coexistence with the previous standard. For HEW,the same requirement exists for coexistence with legacy devices andsystems.

Thus there are general needs for systems and methods that that allow HEWdevices to coexist with legacy devices that operate in accordance withprior versions of the standards. There are general needs for systems andmethods that that allow HEW communications to be distinguished fromlegacy communications and provide coexistence with legacy devices andsystems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless network in accordance with someembodiments;

FIG. 2A illustrates a non-HT (high-throughput) format packet protocoldata unit (PPDU) in accordance with some embodiments;

FIG. 2B illustrates a HT mixed-format PPDU in accordance with someembodiments;

FIG. 2C illustrates a VHT (very-high throughput) format PPDU inaccordance with some embodiments;

FIG. 2D illustrates a HEW format PPDU in accordance with someembodiments;

FIG. 2E illustrates a HEW format PPDU for single-stream transmissions inaccordance with some embodiments;

FIG. 2F illustrates a HEW format PPDU for multi-stream transmissionswith transmit beamforming in accordance with some alternate embodiments;

FIG. 2G illustrates a HEW format PPDU for multi-stream transmissionswithout transmit beamforming in accordance with some embodiments;

FIG. 3 illustrates signal field constellations in accordance with someembodiments;

FIG. 4 is a procedure for configuring a PPDU for communicating with HEWstations and legacy stations in accordance with some embodiments; and

FIG. 5 is a block diagram of an HEW device in accordance with someembodiments.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

Embodiments disclosed herein provide for coexistence of High EfficiencyWi-Fi (HEW) devices with existing legacy Wi-Fi devices. Legacy devicesmay refer to devices operating in accordance with previous Wi-Fistandards and/or amendments such as IEEE 802.11g/a, IEEE 802.11n or IEEE802.11ac. HEW is a recent activity in IEEE to evolve the Wi-Fi standard.It has several target use cases, with a large focus on improving systemefficiency in dense deployed networks. Since it is an evolution of theprevious standards and needs to coexist with the legacy systems, atechnique to identify each transmission as either a HEW packet or alegacy packet is needed. Additionally, it would be advantageous if thetechnique to identify the HEW transmissions could at the same time deferlegacy devices. Finally, since one focus on HEW is efficiency, anotheraspect is to have a mechanism which accomplishes these things withoutadding any additional overhead to each transmission and possiblyreducing the overhead.

Embodiments disclosed herein provide techniques to notify HEW devicesthat an HEW compliant transmission is occurring while also deferringlegacy devices and doing so with little or no additional overhead fromwhat is done in legacy transmissions and in some embodiments, lessoverhead. Since HEW is an evolution of the existing Wi-Fi standards,there have not been any previous solutions to address this need.

In some embodiments, the preamble portion of the packet has beenincreased and new fields added with various modulation formats so thatthe new releases could be identified. Some embodiments described hereinare configured to defer legacy devices using the legacy signal field(L-SIG) and build upon the coexistence approach adopted in IEEE 802.11nand IEEE 802.11ac. In those systems, the rate field of the L-SIG wasfixed to a set known value and the length was set to a length that woulddefer those devices beyond the transmission of an IEEE 802.11n or anIEEE 802.11ac transmission.

In some embodiments disclosed herein, the same fixed value in the ratefield may be used although this is not a requirement. In someembodiments, the length field of the L-SIG may be computed differentlyfrom what is done in an IEEE 802.11n/ac system to allow deferral oflegacy systems and identification of an HEW transmission. Theseembodiments are described in more detail below.

Following the L-SIG in an IEEE 802.11n/ac transmission are additionalSIG fields. In IEEE 802.11n/ac systems, these SIG fields follow directlyafter the L-SIG and are phase rotated in order to allow identification.In the embodiments disclosed herein, an HEW signal field may also beused if needed and may use a modified legacy length value allowing forseveral preamble designs and potentially several payloads to support notonly single user (SU) packets to multi-user (MU) packets like multi-usermultiple-input multiple-output (MU-MIMO) or orthogonal frequencydivision multiple access (OFDMA). In these embodiments that use uplinkMU-MIMO or uplink OFDMA, an access point (AP) may operate as a masterstation which would have mechanisms to contend and hold the medium.Uplink transmissions from scheduled HEW stations may immediately follow.In those cases, the AP may signal the specific devices that are targetedfor uplink transmission the transmission parameters. Therefore, eachdevice that transmits in the uplink would not need to send anyadditional configuration parameters and therefore does not need anadditional SIG field in the preamble during their transmission.

Embodiments disclosed herein also allow legacy devices that missed theinitial AP transmission (e.g., when returning from a power save mode) todetect the signal and properly defer irrespective of them being an IEEE802.11a, an IEEE 802.11n or an IEEE 802.11ac device. In theseembodiments, a new signal field modulation format is disclosed in whichthe first symbol is set as rotated BPSK (i.e., rotated by 90 degrees)and then the second would be BPSK (i.e., not rotated). These embodimentsare described in more detail below.

FIG. 1 illustrates a wireless network in accordance with someembodiments. Wireless network 100 may include a master station (STA)102, a plurality of HEW stations 104 (i.e., HEW devices), and aplurality of legacy stations 106 (legacy devices). The master station102 may be arranged to communicate with the HEW stations 104 and thelegacy stations 106 in accordance with one or more of the IEEE 802.11standards. In some embodiments, the master station 102 may be an accesspoint (AP), although the scope of the embodiments is not limited in thisrespect.

Legacy stations 106 may include, for example, non-HT stations 108 (e.g.,IEEE 802.11a/g stations), HT stations 110 (e.g., IEEE 802.11n stations),and VHT stations 112 (e.g., IEEE 802.11ac stations). Embodimentsdisclosed herein allow HEW stations 104 to distinguish transmissions(e.g., packets such as packet protocol data units (PPDUs)) fromtransmissions of legacy stations 106 and cause legacy stations 106 to atleast defer their transmissions during HEW transmissions providingbackwards compatibility. In some embodiments, the length field of thelegacy signal field (L-SIG) may be used to cause some legacy stations106 to defer transmissions. In some embodiments, the length field of theL-SIG may be used to distinguish HEW PPDUs from non-HEW PPDUs. In someembodiments, a phase rotation applied to a subsequent or additionalsignal field (an HT-SIG, a VHT SIG or an HEW SIG) may be used todistinguish HT PPDUs, VHT PPDUs and HEW PPDUs. In some embodiments, therate field of the L-SIG may be used to cause some legacy stations 106 todefer transmissions and distinguish non-HT transmissions from HT, VHTand HEW transmissions. These embodiments are discussed in more detailbelow.

In accordance with embodiments, the master station 102 may includehardware processing circuitry including physical layer (PHY) andmedium-access control layer (MAC) circuitry which may be arranged tocontend for a wireless medium (e.g., during a contention period) toreceive exclusive control of the medium for an HEW control period (i.e.,a transmission opportunity (TXOP)). The master station 102 may transmitan HEW master-sync transmission at the beginning of the HEW controlperiod. During the HEW control period, the HEW stations 104 maycommunicate with the master station 102 in accordance with anon-contention based multiple-access technique (e.g., an OFDMA techniqueor MU-MIMO technique). This is unlike conventional Wi-Fi communicationsin which devices communicate in accordance with a contention-basedcommunication technique, rather than a non-contention multiple-accesstechnique. During the HEW control period, legacy stations 106 refrainfrom communicating and defer their transmissions. In some embodiments,the HEW master-sync transmission may be referred to as an HEW controland schedule transmission.

In accordance with some embodiments, the master-sync transmission mayinclude a multi-device HEW preamble arranged to signal and identify datafields for a plurality of scheduled HEW stations 104. The master station102 may further be arranged to transmit (in the downlink direction)and/or receive (in the uplink direction) one or more of the data fieldsto/from the scheduled HEW stations 104 during the HEW control period. Inthese embodiments, the master station 102 may include training fields inthe multi-device HEW preamble to allow each of the scheduled HEWstations 104 to perform an initial channel estimate.

In accordance with some embodiments, an HEW station 104 may be an IEEE802.11ax configured station (STA) that is configured for HEW operation.An HEW station 104 may be configured to communicate with a masterstation 102 in accordance with a scheduled multiple access techniqueduring the HEW control period and may be configured to receive anddecode the multi-device HEW preamble of an HEW frame or PPDU. An HEWstation 104 may also be configured to decode an indicated data fieldreceived by the master station 102 during the HEW control period.Examples of HEW PPDUs are illustrated in FIGS. 2D through 2G discussedbelow.

In accordance with some embodiments, the master station 102 may bearranged to select a number of HEW long-training fields (LTFs) to beincluded in the multi-device HEW preamble of an HEW frame. The HEW framemay comprise a plurality of links for transmission of a plurality ofdata streams. The master station 102 may also transmit the selectednumber of LTFs sequentially as part of the multi-device HEW preamble.The master station 102 may also transmit/receive a plurality of datafields sequentially to/from each of a plurality of scheduled HEWstations 104. The data fields may be part of the HEW frame. Each datafield may correspond to one of the links and may comprise one or moredata streams. In some embodiments, the data fields may be separatepackets. The master station 102 may also be arranged receive packetsfrom HEW stations 104 in the uplink direction during the HEW controlperiod.

In some embodiments, the selection of the number of LTFs to be includedin the multi-device HEW preamble may be based on a maximum number ofstreams to be transmitted on a single link. In some embodiments, theselection of the number of LTFs to be included in the multi-device HEWpreamble may be based on a scheduled HEW station 104 with a greatestchannel estimation need (e.g., the scheduled HEW station 104 receivingthe greatest number of streams on a single link). In some embodiments,the selection of the number of LTFs to be included in the multi-deviceHEW preamble may be based on the sum of greatest number of streams oneach single link that scheduled HEW stations 104 would receive. In someembodiments, the number of LTFs to be included in the multi-device HEWpreamble may be predetermined. In these embodiments, the number of LTFsto be included in the multi-device HEW preamble may be based on themaximum number of streams that can be transmitted on a single link.

In some embodiments, the master station 102 may be arranged to configurethe multi-device HEW preamble include an HEW control signal field (i.e.,HEW SIG-B) to identify and signal each of the data fields of the HEWframe. In these embodiments, a single HEW preamble is included in an HEWframe, which is unlike conventional techniques which include a preamblefor each link.

FIG. 2A illustrates a non-HT format PPDU in accordance with someembodiments. The non-HT format PPDU may be used for communicating withnon-HT stations 108 (FIG. 1), which may include stations configured tocommunicate in accordance with an IEEE 802.11a or IEEE 802.11g standard.In IEEE 802.11a/g, the packet structure comprises a Legacy ShortTraining Field (L-STF) 202, a Legacy Long Training Field (L-LTF) 204 andthe L-SIG 206 which made up the preamble. The preamble is followed by adata field 208. The L-SIG 206 provides information about the data field208 including the coding and modulation (rate) and the length.

FIG. 2B illustrates a HT mixed-format PPDU in accordance with someembodiments. The HT mixed-format PPDU may be used for communicating withHT stations 110 (FIG. 1), which may include stations configured tocommunicate in accordance with an IEEE 802.11n standard. In IEEE802.11n, the packet structure allows the IEEE 802.11n devices to coexistwith IEEE 802.11a/g devices and therefore included the legacy preambleportion of the packet to be used at the beginning of the transmission.The IEEE 802.11n transmission sets the rate field of the L-SIG 206 to afixed rate and the length field is set to extend for the full durationof the IEEE 802.11n packet. Following the legacy portion of thepreamble, the IEEE 802.11n preamble includes a HT-SIG 212 for the IEEE802.11n and includes additional configuration information for thosedevices. The HT-SIG 212 uses rotated binary phase-shift keying (BPSK) inboth symbols of the HT-SIG 212 so that IEEE 802.11n devices candistinguish it from non-rotated BPSK data 208 of an IEEE 802.11a/gtransmission and allows those devices to detect the existence of an IEEE802.11n packet. Thus, IEEE 802.11a/g devices are able to recognize thelegacy portion of the preamble, but not the portion following the legacyportion and may defer based on the configuration parameters in the L-SIG206 of the HT mixed-format PPDU of FIG. 2B assuring coexistence.

FIG. 2C illustrates a VHT format PPDU in accordance with someembodiments. The VHT format PPDU may be used for communicating with VHTstations 112 (FIG. 1), which may include stations configured tocommunicate in accordance with an IEEE 802.11ac standard. In 802.11ac,the packet also starts with the legacy portion of the preamble which isthen followed by a VHT-SIG 222 to provide additional configurationparameters for the VHT data field. The IEEE 802.11a/g devices recognizethe legacy portion of the packet but would decode the rest of the packetcorrectly and thus defer from transmission for the full length based onthe legacy rate/length fields.

IEEE 802.11ac devices are also able to discern IEEE 802.11ac packetsfrom other legacy (IEEE 802.11a/g and IEEE 802.11n) packets. In thediscussion above regarding IEEE 802.11n, the HT-SIG field 212 (FIG. 2B)following the L-SIG 206 is modulated using BPSK as in the L-SIG 206, butit is rotated 90 degrees. This modulation format may be used by an IEEE802.11n device to detect those packets and identify them as IEEE 802.11npackets. For IEEE 802.11ac devices to detect IEEE 802.11ac packets, theVHT-SIG 222 (FIG. 2C) is normal BPSK for the first symbol of the VHT-SIG222 and is rotated 90 degrees for the second symbol. This allows for theidentification of IEEE 802.11ac packets by IEEE 802.11ac devices, butdemodulation of the VHT-SIG 222 may not be possible by the IEEE 802.11ndevices. In those cases the IEEE 802.11n device will defer based on theL-SIG 206.

FIGS. 2D-2G illustrate HEW format PPDUs in accordance with variousembodiments. The HEW formats PPDU of FIGS. 2D-2G may be used forcommunicating with HEW stations 104 (FIG. 1), which may include stationsconfigured to communicate in accordance with an IEEE 802.11x standard.In accordance with embodiments, the master station 102 (FIG. 1) mayconfigure a PPDU comprising a legacy signal field (L-SIG) 206 followinglegacy training fields (i.e., L-STF 202 and L-LTF 204).

In some embodiments, the L-SIG 206 may be configured to include at leasta length field and a rate field. The master station 102 may select avalue for the length field that is non-divisible by three forcommunicating with the HEW stations 104 and may select a value for thelength field that is divisible by three for communicating with at leastsome legacy stations 106. In these embodiments, when the length field isnot divisible by three, at least some legacy stations 106 (i.e., HTstations 110 and VHT stations 112) would determine that the length fieldvalue in the L-SIG 206 is invalid and will properly defer theirtransmissions. When the length field is not divisible by three, HEWstations 104 may be configured to identify the PPDU as an HEW PPDU anddecode one or more of the fields that follow the L-SIG 206.

In some embodiments, the master station 102 is further arranged toconfigure the L-SIG 206 with a valid parity bit (i.e., the L-SIG paritybit) when the length field is selected to be divisible by three and whenthe length field is selected to be non-divisible by three. In theseembodiments, the L-SIG may always be configured with a valid parity bit.In these embodiments, when a valid L-SIG parity bit is indicated, thephysical layer (PHY) of a device may maintain a busy indication for thepredicted duration of the PPDU. Thus legacy stations 106 will defer forthe value indicated by the length (L_LENGTH) field in the L-SIG 206 evenif the value is invalid (i.e., not divisible by three) as long as theparity bit is valid.

In some embodiments, the master station 102 may multiply a ceilingfunction by three and subtract either two or one to calculate the valuefor the length field for the HEW PPDUs. By multiplying the ceilingfunction by three and then subtracting two or one assures that thelength field is not divisible by three. The master station 102 maymultiply the ceiling function by three and subtract three to calculatethe value for the length field for HT and VHT PPDUs. By multiplying theceiling function by three and then subtracting three assures that thelength field is divisible by three. These embodiments are discussed inmore detail below.

In some embodiments, the length calculation used to populate the L-SIGfor 0.11ac packets is give as (L_LENGTH):

${{TXTIME}( {{for}\mspace{14mu} {SGI}} )} = {T_{LEG\_ PREAMBLE} + T_{L - {SIG}} + T_{{VHT} - {SIG} - A} + T_{VHT\_ PREAMBLE} + T_{{VHT} - {SIG} - B} + {T_{SYM} \times \lceil \frac{T_{SYMS} \times N_{SYM}}{T_{SYM}} \rceil}}$${L\_ LENGTH} = {{\lceil \frac{{TXTIME} - 20}{4} \rceil \times 3} - 3}$

In the above equations, the T variable is the time for the respectiveportions of the packet and variables T_(SYMS), T_(SYM) and N_(SYM)represent the short GI symbol interval, symbol interval and number ofsymbols in a packet respectively. The equation in the L_LENGTHcalculation uses a ceiling function multiplied by three and then threeis subtracted. For any value of TXTIME, the L_LENGTH will be divisibleby three. Thus, for HEW packets, embodiments disclosed herein may setthe L_LENGTH to a value that is not divisible by three. In someembodiments, the expression for L_LENGTH for HEW packets may be:

$L_{LENGTH} = {{\lceil \frac{{TXTIME} - 20}{4} \rceil \times 3} - 2}$

This would result in a length that is one larger than before but is notdivisible by three. Doing this may be sufficient to identify HEW packetsand may allow coexistence with legacy (IEEE 802.11a/g/n/ac) devices.Legacy stations 106 would decode the L-SIG, and defer for a time basedon the L_LENGTH value regardless of the value.

In these embodiments, no additional signaling or other metrics need tobe added in order to identify HEW packets. That is very appealing in HEWwhere efficiency is a key design parameter. Additionally, for techniqueslike uplink MU-MIMO and OFDMA to be efficient a very short preamble isdesirable. These embodiments are very efficient with no overhead andprovide full coexistence with legacy systems.

In some embodiments, the master station 102 may be arranged to configurethe PPDU to include a subsequent/additional signal field 210 (e.g.,HT-SIG 212, VHT-SIG 222, or HEW-SIG 232) following the L-SIG 206. Thesubsequent signal field 210 may have first and second symbols that areBPSK modulated. In these embodiments, the master station 102 may selecta phase rotation for application to the BPSK modulation of at least oneof the first and second symbols of the subsequent signal field 210 todistinguish a HT PPDU (FIG. 2B), a VHT PPDU (FIG. 2C) and an HEW PPDU(FIGS. 2D-2G). These embodiments are discussed in more detail below.

In some embodiments, for communicating with HEW stations 104, the masterstation 102 may configure the PPDU to include a number of long-trainingfields (LTFs) 234 to be included in a multi-device HEW preamble thePPDU. The number of LTFs 234 may be based on a maximum number of streamscommunicated over a link. The master station 102 may contend for awireless medium during a contention period to receive control of themedium for an HEW control period (i.e., a TXOP) and may transmit thePPDU during the HEW control period. During the HEW control period, themaster station 102 may operate as a master station having exclusive useof the wireless medium for communication of data with a plurality ofscheduled HEW stations 104 in accordance with a non-contention basedscheduled OFDMA technique in accordance with signaling informationindicated in an HEW signal field. The scheduled OFDMA technique may, forexample, be an uplink (UL) OFDMA technique, a downlink (DL) OFDMAtechnique or an UL or DL multi-user multiple-input multiple-output(MU-MIMO) technique.

In some embodiments, for an HEW PPDU, each data field may be associatedwith either a single user (SU) link or a multi-user (MU) link and eachlink may be configurable to provide multiple streams of data. The linksof the HEW PPDU may be configurable to have a bandwidth of one of 20MHz, 40 MHz, 80 MHz or 160 MHz.

FIG. 2E illustrates a HEW format PPDU for single-stream transmissions inaccordance with some embodiments. In these embodiments, all signalinginformation for transmission of a single stream over a link may beincluded within the HEW-SIG 232 eliminating the need for one or more HEWLTFs and an HEW SIG B field. The multi-stream HEW format PPDU of FIG.2D, on the other hand includes a number of LTFs 234 based on a maximumnumber of streams communicated over a link and an HEW SIG-B field.

FIG. 2F illustrates a HEW format PPDU for multi-stream transmissionswith transmit beamforming in accordance with some embodiments. In theseembodiments, the signaling information from the HEW-SIG-B field may beincluded within the HEW-SIG 232 eliminating the need for a second signalfield (e.g., an HEW SIG B field). In these embodiments, the number ofHEW LTFs 234 may be based on a maximum number of streams communicatedover the link and an HEW STF 233 may be included for transmitbeamforming.

FIG. 2G illustrates a HEW format PPDU for multi-stream transmissionswithout transmit beamforming in accordance with some embodiments. Inthese embodiments, the signaling information from the HEW-SIG-B fieldmay be included within the HEW-SIG 232 eliminating the need for a secondsignal field (e.g., an HEW SIG B field). In these embodiments, thenumber of HEW LTFs 234 may be based on a maximum number of streamscommunicated over the link and an HEW STF may not be needed sincetransmit beamforming is not performed.

FIG. 3 illustrates signal field constellations in accordance with someembodiments. As illustrated in FIG. 3, the L-SIG 206 for non-HT stations108, for HT stations 110, for VHT stations 112 and for HEW stations 104is illustrated with conventional BPSK modulation (i.e., no phaserotation is applied). As further illustrated in FIG. 3, a selected phaserotation for application to the BPSK modulation of the first and secondsymbols of the subsequent signal field 210 is shown.

In accordance with embodiments, for communicating with the HEW stations104, the subsequent signal field 210 may be an HEW signal field(HEW-SIG) 232 (FIGS. 2D-2G) and the master station 102 may apply aninety-degree phase rotation to the BPSK modulation of the first symbol332A of the HEW-SIG 232 (i.e., rotated BPSK) and may refrain fromapplying a ninety-degree phase rotation to the BPSK modulation of thesecond symbol 332B of the HEW-SIG 232. Accordingly, for an HEW-PPDU, thefirst symbol 332A of the HEW-SIG 232 is rotated BPSK and the secondsymbol 332B is conventional (i.e., non-rotated) BPSK.

For communicating with VHT stations 112, the subsequent signal field 210may be an VHT signal field (VHT-SIG) 222 (FIG. 2C) and the masterstation 102 may refrain from applying a ninety-degree phase rotation tothe BPSK modulation of the first symbol 322A of the VHT-SIG 222 and mayapply a ninety-degree phase rotation to the BPSK modulation of thesecond symbol 322B of the VHT-SIG 222. Accordingly, for a VHT-PPDU, thefirst symbol 322A of the VHT-SIG 222 is conventional BPSK and the secondsymbol 322B is rotated BPSK.

For communicating with HT stations 110, the subsequent signal field 210may be an HT signal field (HT-SIG) 212 (FIG. 2B) and the master station102 may apply a ninety-degree phase rotation to the BPSK modulation ofboth the first symbol 312A and the second symbol 312B of the HT-SIG 222.Accordingly, for a HT PPDU, both symbols of the HT-SIG 222 are rotatedBPSK.

For communicating with non-HT stations 108, the access point may refrainfrom including the subsequent signal field 210 following the L-SIG 206.The data field 208 of a non-HT PPDU may have conventional (non-phaserotated) modulation (e.g., BPSK to 64QAM) applied for all symbolsallowing a non-HT PPDU to be identified and distinguished from other HT,VHT and HEW PPDUs.

In accordance with some embodiments, the phase rotation of the symbolsin the subsequent signal field 210 may be used to distinguish an HEWPPDU from a non-HEW PPDU, such as a HT PPDU or a VHT PPDU. In theseembodiments, it may not be necessary to use the length field of theL-SIG 206 to distinguish an HEW PPDU from a non-HEW PPDU and the lengthfield may be set to a value that is divisible by three, although thescope of the embodiments is not limited in this respect. In someembodiments, the length field may also be used to distinguish an HEWPPDU from a non-HEW PPDU, such as a HT PPDU or a VHT PPDU.

In some embodiments, for communicating with the HEW stations 104 andsome legacy stations 106 including HT stations 110 and VHT stations 112,the master station 102 may select a value for the rate field to causethe non-HT stations 108 to defer transmissions. In these embodiments,the non-HT stations 108 may correctly decode the L-SIG 206 but may beunable to correctly decode the remainder of the PPDU based on theindicated rate (or the cyclic-redundancy check (CRC) may fail) causingthese stations to ignore the PPDU but defer based on the lengthindicated in the length field of the L-SIG 206. In these embodiments, apredetermined value (e.g., 5 or 6) may be selected for the rate fieldwhich may cause the non-HT stations 108 to defer their transmissionsbecause of their inability to decode the subsequent fields.

FIG. 4 is a procedure for configuring a PPDU for communicating with HEWstations and legacy stations in accordance with some embodiments.Procedure 400 may be performed by an access point, such as masterstation 102 (FIG. 1), for communicating with HEW stations 104 (FIG. 1)as well as legacy stations 106 (FIG. 1).

In operation 402, a PPDU is configured to include one or more legacytraining fields and a legacy signal field (L-SIG) 206 following thelegacy training fields.

In operation 404, the L-SIG 206 is configured to include at least alength field.

In operation 406, a value for the length field that is not divisible bythree is selected for communicating with the HEW stations 104.

In operation 408, a value for the length field that is divisible bythree is selected for communicating with at least some legacy stations106.

In operation 410, the PPDU is configured to include an additional signalfield following the L-SIG 206.

In operation 412, a phase rotation is selected for application to theBPSK modulation of at least one of the first and second symbols of theadditional signal field to distinguish a HT PPDU, a VHT PPDU and an HEWPPDU.

In some embodiments, operation 412 may be optional as the value selectedfor the length field in operations 406 and 408 may be used todistinguish HEW from non-HEW PPDUs. In some alternate embodiments, thevalue for the length field that is divisible by three is selected forcommunicating with all stations and the phase rotation of the symbols ofthe additional signal field may be used to distinguish a HT PPDU, a VHTPPDU and an HEW PPDU.

FIG. 5 illustrates an HEW device in accordance with some embodiments.HEW device 500 may be an HEW compliant device that may be arranged tocommunicate with one or more other HEW devices, such as HEW stations 104(FIG. 1) or master station 102 (FIG. 1) as well as communicate withlegacy stations 106 (FIG. 1). HEW device 500 may be suitable foroperating as master station 102 (FIG. 1) or an HEW station 104 (FIG. 1).In accordance with embodiments, HEW device 500 may include, among otherthings, physical layer (PHY) circuitry 502 and medium-access controllayer circuitry (MAC) 504. PHY 502 and MAC 504 may be HEW compliantlayers and may also be compliant with one or more legacy IEEE 802.11standards. MAC 504 may be arranged to configure PPDUs in accordance withone or more of FIGS. 2A-2G and PHY 502 may be arranged to transmit andreceive PPDUs, among other things. HEW device 500 may also include otherhardware processing circuitry 506 and memory 508 configured to performthe various operations described herein.

In accordance with some embodiments, when operating as an HEW station104, the HEW device 500 may be arranged to distinguish an HEW PPDU froma non-HEW PPDU based at least in part on a value in a length field inthe L-SIG 206 (FIGS. 2A-2G). In these embodiments, the HEW device 500may be configured to receive L-SIG 206 following legacy training fields(i.e., L-STF 202 and L-LTF 204). The L-SIG 206 may include the lengthfield and a rate field. The HEW device 500 may determine whether a valuefor the length field is divisible by three and verify a parity bit ofthe L-SIG. The HEW device 500 may identify the PPDU as an HEW PPDU whenthe value in the length field is not divisible three and the parity bitis verified, and may identify the PPDU as a non-HEW PPDU (e.g., a VHTPPDU or HT PPDU) when the value in the length field is divisible threeand the parity bit is verified. In some embodiments, the HEW device 500may also be configured to decode subsequent fields of the PPDU whenidentified as an HEW PPDU and refrain from decoding subsequent fields ofthe PPDU when the PPDU is identified as a non-HEW PPDU.

In some embodiments, when operating as an HEW station 104, the HEWdevice 500 may be arranged to distinguish an HEW PPDU from a non-HEWPPDU based on the phase rotation of symbols of a subsequent signalfield. In these embodiments, the HEW device 500 may be configured toreceive an L-SIG 206 and receive a subsequent signal field 210 (HT-SIG212, VHT-SIG 222, or HEW-SIG 232). The subsequent signal field 210 mayhave first and second symbols that are BPSK modulated. In theseembodiments, the HEW device 500 may determine whether the PPDU is a HTPPDU, a VHT PPDU or an HEW PPDU based on the phase rotation applied tothe BPSK modulation of at least one of the first and second symbols ofthe subsequent signal field 210. For an HEW PPDU, a ninety-degree phaserotation may have been applied to the BPSK modulation of the firstsymbol 332A and no phase rotation would have been applied to the BPSKmodulation of the second symbol 332B of the subsequent signal field 210.

In accordance with some embodiments, the MAC 504 may be arranged tocontend for a wireless medium during a contention period to receivecontrol of the medium for the HEW control period and configure an HEWPPDU (e.g., FIG. 2D). The PHY 502 may be arranged to transmit the HEWPPDU as discussed above. The PHY 502 may include circuitry formodulation/demodulation, upconversion/downconversion, filtering,amplification, etc. In some embodiments, the hardware processingcircuitry 506 may include one or more processors. In some embodiments,two or more antennas may be coupled to the PHY 502 and arranged forsending and receiving signals including transmission of the HEW packets.The memory 508 may be store information for configuring the othercircuitry to perform operations for configuring and transmitting HEWpackets and performing the various operations described herein.

In some embodiments, the HEW device 500 may be configured to communicateusing OFDM communication signals over a multicarrier communicationchannel. In some embodiments, HEW device 500 may be configured tocommunicate in accordance with one or more specific communicationstandards, such as the Institute of Electrical and Electronics Engineers(IEEE) standards including IEEE 802.11-2012, 802.11n-2009,802.11ac-2013, 802.11ax standards and/or proposed specifications forWLANs, although the scope of the invention is not limited in thisrespect as they may also be suitable to transmit and/or receivecommunications in accordance with other techniques and standards.

In some embodiments, the HEW device 500 may be part of a portablewireless communication device, such as a personal digital assistant(PDA), a laptop or portable computer with wireless communicationcapability, a web tablet, a wireless telephone or smartphone, a wirelessheadset, a pager, an instant messaging device, a digital camera, anaccess point, a television, a medical device (e.g., a heart ratemonitor, a blood pressure monitor, etc.), or other device that mayreceive and/or transmit information wirelessly. In some embodiments, theHEW device 500 may include one or more of a keyboard, a display, anon-volatile memory port, multiple antennas, a graphics processor, anapplication processor, speakers, and other mobile device elements. Thedisplay may be an LCD screen including a touch screen.

The antennas of the HEW device 500 may comprise one or more directionalor omnidirectional antennas, including, for example, dipole antennas,monopole antennas, patch antennas, loop antennas, microstrip antennas orother types of antennas suitable for transmission of RF signals. In someMIMO embodiments, the antennas may be effectively separated to takeadvantage of spatial diversity and the different channel characteristicsthat may result between each of antennas and the antennas of atransmitting station.

Although the HEW device 500 is illustrated as having several separatefunctional elements, one or more of the functional elements may becombined and may be implemented by combinations of software-configuredelements, such as processing elements including digital signalprocessors (DSPs), and/or other hardware elements. For example, someelements may comprise one or more microprocessors, DSPs,field-programmable gate arrays (FPGAs), application specific integratedcircuits (ASICs), radio-frequency integrated circuits (RFICs) andcombinations of various hardware and logic circuitry for performing atleast the functions described herein. In some embodiments, thefunctional elements of the HEW device 500 may refer to one or moreprocesses operating on one or more processing elements.

Embodiments may be implemented in one or a combination of hardware,firmware and software. Embodiments may also be implemented asinstructions stored on a computer-readable storage device, which may beread and executed by at least one processor to perform the operationsdescribed herein. A computer-readable storage device may include anynon-transitory mechanism for storing information in a form readable by amachine (e.g., a computer). For example, a computer-readable storagedevice may include read-only memory (ROM), random-access memory (RAM),magnetic disk storage media, optical storage media, flash-memorydevices, and other storage devices and media. Some embodiments mayinclude one or more processors and may be configured with instructionsstored on a computer-readable storage device.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims. The following claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparate embodiment.

What is claimed is:
 1. An access point (AP) arranged for communicatingwith a plurality of stations (STAs) including high-efficiency Wi-Fi(HEW) stations and legacy stations, the access point comprising hardwareprocessing circuitry and physical layer (PHY) circuitry to: configure apacket protocol data unit (PPDU) comprising a legacy signal field(L-SIG) following legacy training fields, the L-SIG including at least alength field and a rate field; select a value for the length field thatis not-divisible by three for communicating with the HEW stations; andselect a value for the length field that is divisible by three forcommunicating with at least some of the legacy stations.
 2. The accesspoint of claim 1 wherein the access point is further arranged toconfigure the L-SIG with a valid parity bit when the length field isselected to be divisible by three and when the length field is selectedto be non-divisible by three.
 3. The access point of claim 2 wherein,the access point is further arranged to configure the PPDU to include asubsequent signal field following the L-SIG, the subsequent signal fieldhaving first and second symbols that have BPSK modulation, and whereinthe access point is further arranged to select a phase rotation forapplication to the BPSK modulation of at least one of the first andsecond symbols of the subsequent signal field to distinguish ahigh-throughput (HT) PPDU, a very-high throughput (VHT) PPDU and an HEWPPDU.
 4. The access point of claim 3 wherein for communicating with theHEW stations, the subsequent signal field is an HEW signal field(HEW-SIG) and the access point is arranged to apply a ninety-degreephase rotation to the BPSK modulation of the first symbol of the HEW-SIGand refrain from applying a ninety-degree phase rotation to the BPSKmodulation of the second symbol of the HEW-SIG.
 5. The access point ofclaim 4 wherein for communicating with VHT stations, the subsequentsignal field is an VHT signal field (VHT-SIG) and the access point isarranged to apply a ninety-degree phase rotation to the BPSK modulationof the second symbol of the VHT-SIG and refrain from applying aninety-degree phase rotation to the BPSK modulation of the first symbolof the VHT-SIG, wherein for communicating with HT stations, thesubsequent signal field is an HT signal field (HT-SIG) and the accesspoint is arranged to apply a ninety-degree phase rotation to the BPSKmodulation of both the first symbol and the second symbol of the HT-SIG,and wherein for communicating with non-HT stations, the access point isconfigured to refrain from including the subsequent signal fieldfollowing the L-SIG.
 6. The access point of claim 5 wherein forcommunicating with the HEW stations and some legacy stations includingHT stations and VHT stations, the access point is arranged to select avalue for the rate field to cause the non-HT stations to defertransmissions.
 7. The access point of claim 1 wherein the access pointis configured to multiply a ceiling function by three and subtracteither two or one to calculate the value for the length field for theHEW stations, and wherein the access point is configured to multiply theceiling function by three and subtract three to calculate the value forthe length field for non-HEW stations.
 8. The access point of claim 4wherein for communicating with HEW stations, the access point is furtherconfigured to: configure the PPDU as an HEW PPDU to include a number oflong-training fields (LTFs), the number of LTFs being based on a maximumnumber of streams communicated over a link; contend for a wirelessmedium during a contention period to receive control of the medium foran HEW control period; and transmit the HEW PPDU during the HEW controlperiod, wherein during the HEW control period, the access point operatesas a master station having exclusive use of the wireless medium forcommunication of data with a plurality of scheduled HEW stations inaccordance with a non-contention based scheduled orthogonal frequencydivision multiple access (OFDMA) technique in accordance with signalinginformation indicated in the HEW-SIG, wherein the scheduled OFDMAtechnique is one of an uplink OFDMA technique, a downlink OFDMAtechnique or a multi-user multiple-input multiple-output (MU-MIMO)technique.
 9. The access point of claim 8 wherein for the HEW PPDU, eachdata field is associated with either a single user (SU) link or amulti-user (MU) link, each link configurable to provide multiple streamsof data, and wherein the links of the HEW PPDU are configurable to havea bandwidth of one of 20 MHz, 40 MHz, 80 MHz or 160 MHz.
 10. An accesspoint arranged for communicating with a plurality of stations includinghigh-efficiency Wi-Fi (HEW) stations and legacy stations, the accesspoint comprising hardware processing circuitry and physical layer (PHY)circuitry to configure a packet protocol data unit (PPDU) comprising: alegacy signal field (L-SIG) following one or more legacy trainingfields; and one or more fields following the L-SIG including asubsequent signal field, the subsequent signal field having first andsecond symbols that have BPSK modulation, wherein the access point isfurther arranged to select a phase rotation for application to the BPSKmodulation of at least one of the first and second symbols of thesubsequent signal field to distinguish a high-throughput (HT) PPDU, avery-high throughput (VHT) PPDU and an HEW PPDU.
 11. The access point ofclaim 10 wherein for communicating with the HEW stations, the subsequentsignal field is an HEW signal field (HEW-SIG) and the access point isarranged to apply a ninety-degree phase rotation to the BPSK modulationof the first symbol of the HEW-SIG and refrain from applying aninety-degree phase rotation to the BPSK modulation of the second symbolof the HEW-SIG.
 12. The access point of claim 11 wherein forcommunicating with VHT stations, the subsequent signal field is an VHTsignal field (VHT-SIG) and the access point is arranged to apply aninety-degree phase rotation to the BPSK modulation of the second symbolof the VHT-SIG and refrain from applying a ninety-degree phase rotationto the BPSK modulation of the first symbol of the VHT-SIG, wherein forcommunicating with HT stations, the subsequent signal field is an HTsignal field (HT-SIG) and the access point is arranged to apply aninety-degree phase rotation to the BPSK modulation of both the firstsymbol and the second symbol of the HT-SIG, and wherein forcommunicating with non-HT stations, the access point is configured torefrain from including the subsequent signal field following the L-SIG.13. A high-efficiency Wi-Fi (HEW) station arranged to distinguish an HEWpacket protocol data unit (PPDU) from a non-HEW PPDU, the HEW stationcomprising hardware processing circuitry and physical layer (PHY)circuitry configured to: receive a legacy signal field (L-SIG) followinglegacy training fields, the L-SIG including at least a length field anda rate field; determine whether a value for the length field isdivisible by three; verify a parity bit of the L-SIG; identify the PPDUas an HEW PPDU when the value in the length field is not divisible threeand the parity bit is verified; and identify the PPDU as a non-HEW PPDUwhen the value in the length field is divisible three and the parity bitis verified.
 14. The HEW station of claim 12 wherein the HEW station isfurther configured to: decode subsequent fields of the PPDU when thePPDU identified as an HEW PPDU, and refrain from decoding subsequentfields of the PPDU when the PPDU is identified as a non-HEW PPDU.
 15. Ahigh-efficiency Wi-Fi (HEW) station arranged to distinguish an HEWpacket protocol data unit (PPDU) from a non-HEW PPDU, the HEW stationcomprising hardware processing circuitry and physical layer (PHY)circuitry configured to: receive a legacy signal field (L-SIG) followinglegacy training fields, the L-SIG including at least a length field anda rate field; receive a subsequent signal field, the subsequent signalfield having first and second symbols that have BPSK modulation,determine whether the PPDU is a high-throughput (HT) PPDU, a very-highthroughput (VHT) PPDU or an HEW PPDU based on the phase rotation appliedto the BPSK modulation of at least one of the first and second symbolsof the subsequent signal field, wherein for an HEW PPDU, a ninety-degreephase rotation is applied to the BPSK modulation of the first symbol andno phase rotation is applied to the BPSK modulation of the second symbolof the subsequent signal field.
 16. The HEW station of claim 15 whereinwhen an HEW PPDU is determined, the subsequent signal field is anHEW-SIG, and wherein the HEW station is further configured tocommunicate with an HEW master station in accordance with a scheduledOFDMA technique based on information received in the HEW-SIG.
 17. Amethod performed by an access point for communicating with a pluralityof stations including high-efficiency Wi-Fi (HEW) stations and legacystations, the method comprising: configuring a packet protocol data unit(PPDU) comprising a legacy signal field (L-SIG) following legacytraining fields, the L-SIG including at least a length field and a ratefield; selecting a value for the length field that is not-divisible bythree for communicating with the HEW stations; and either selecting avalue for the length field that is divisible by three for communicatingwith at least some of the legacy stations; or selecting a phase rotationfor application to BPSK modulation of at least one of first and secondsymbols of a subsequent signal field to distinguish a high-throughput(HT) PPDU, a very-high throughput (VHT) PPDU and an HEW PPDU.
 18. Themethod of claim 17 further comprising: configuring the PPDU as an HEWPPDU to include a number of long-training fields (LTFs), the number ofLTFs being based on a maximum number of streams communicated over alink; contending for a wireless medium during a contention period toreceive control of the medium for an HEW control period; andtransmitting the HEW PPDU during the HEW control period, wherein duringthe HEW control period, the access point operates as a master stationhaving exclusive use of the wireless medium for communication of datawith a plurality of scheduled HEW stations in accordance with anon-contention based scheduled orthogonal frequency division multipleaccess (OFDMA) technique in accordance with signaling informationindicated in the HEW-SIG, wherein the scheduled OFDMA technique is oneof an uplink OFDMA technique, a downlink OFDMA technique or a multi-usermultiple-input multiple-output (MU-MIMO) technique.
 19. A non-transitorycomputer-readable storage medium that stores instructions for executionby one or more processors of an access point to perform operations forcommunicating with a plurality of stations including high-efficiencyWi-Fi (HEW) stations and legacy stations, the operations to configurethe access point to: configure a packet protocol data unit (PPDU)comprising a legacy signal field (L-SIG) following legacy trainingfields, the L-SIG including at least a length field and a rate field;select a value for the length field that is not-divisible by three forcommunicating with the HEW stations; and either select a value for thelength field that is divisible by three for communicating with at leastsome of the legacy stations; or select a phase rotation for applicationto BPSK modulation of at least one of first and second symbols of asubsequent signal field to distinguish a high-throughput (HT) PPDU, avery-high throughput (VHT) PPDU and an HEW PPDU.
 20. The non-transitorycomputer-readable storage medium of claim 19 wherein the operationsfurther configure the access point to: configure the PPDU as an HEW PPDUto include a number of long-training fields (LTFs), the number of LTFsbeing based on a maximum number of streams communicated over a link;contend for a wireless medium during a contention period to receivecontrol of the medium for an HEW control period; and transmit the HEWPPDU during the HEW control period, wherein during the HEW controlperiod, the access point operates as a master station having exclusiveuse of the wireless medium for communication of data with a plurality ofscheduled HEW stations in accordance with a non-contention basedscheduled orthogonal frequency division multiple access (OFDMA)technique in accordance with signaling information indicated in theHEW-SIG, wherein the scheduled OFDMA technique is one of an uplink OFDMAtechnique, a downlink OFDMA technique or a multi-user multiple-inputmultiple-output (MU-MIMO) technique.